Air conditioning systems that have long since existed as prior art condition the air channeled into the passenger compartment by absorbing the heat required for heating the air mass flow from various heat sources in the heat pump mode or in the reheating mode.
On the one hand, when ambient temperatures are low, for instance, lower than −10° C., air conditioning systems of this type, with coolant-air-heat exchangers which derive their heating action from the coolant circulation system of an efficient combustion engine of the vehicle drive, no longer reach the temperature level necessary for the comfortable heating of the passenger compartment. The same is true for systems in vehicles with a hybrid engine; for these vehicles, the use of reheating concepts is necessary. On the other hand, heat is extracted from the coolant, so that the combustion engine is operated for extended periods at low temperatures, which has a negative effect on exhaust emissions and fuel consumption. Based on the intermittent use of the combustion engine in hybrid vehicles, a sufficiently high coolant temperature is no longer achieved during long drives. As a result, the start-stop operation of the combustion engine is discontinued at low ambient temperatures. The combustion engine is not switched off.
Furthermore, there is a trend towards a full electrification of the engine, for instance in vehicles operated by batteries or fuel cells. In such vehicles, waste heat from the combustion engine is eliminated as a possible source for heating the air.
Moreover, the amount of energy that can be stored in the battery of the vehicle is lower than the amount of energy that can be stored in the form of liquid fuel inside the fuel tank. As a result, the power needed for air conditioning the passenger compartment of an electrically powered vehicle has a considerable effect on the range of the vehicle.
Known from prior art are air conditioning system for vehicles for combined operation in cooling and heat pump mode in order to heat, cool, and dehumidify the conditioned air channeled into the passenger compartment.
Similarly, air conditioning system with a heat pump mode are known, in which the evaporator can be operated as an evaporator in cooling mode as well as in heat pump mode, and in which the condenser can be operated as a condenser in cooling mode as well as in heat pump mode. These air conditioning systems are controlled either via the refrigerant circulation system and/or via the air.
From DE 10 2012 108 891 A1 we learn about an air conditioning system for the conditioning of the air in a passenger compartment. The air conditioning system designed for the cooling and heating of the passenger compartment as well as for reheating features an enclosure with two flow channels for the conduction of air, as well as a refrigerant circulation system with an evaporator and a condenser, wherein the evaporator is located in the first flow channel and the condenser is located in the second flow channel. The setting of the operating mode is solely done via the control of the air flow devices. The heat exchanger, evaporator, or condenser are respectively positioned with a part of the heat transferring surface in the first as well as in the second flow channel, whereas the part of the heat transferring surface necessary for the respective operating mode can be adjusted by means of the air-receiving air flow devices.
The air conditioning system with an enclosure embodied as a single module with in it an integrated refrigerant circulation system features a low weight with short and rigid refrigerant ducts, which prevents external leaks almost entirely. The system is designed to allow switching between various operating modes without switching valves. When in heat pump mode in order to heat the passenger compartment, the air sucked out of the passenger compartment can be used for the evaporation of the refrigerant.
However, preferentially, the system is operated with two blowers, since both the evaporator in the first flow channel and the condenser in the second blow channel, and therefore, each of two independent modules, features one respective blower. The airstream of the vehicle cannot be utilized for the incident flow of the condenser, and therefore, for the heat dissipation from the refrigerant circulation system when operating in cooling mode, so that the blower propagating the air through the second flow channel is continuously in operation. The blower is also operated during the movement of the vehicle, so that the efficiency of the air conditioning system is therefore lower than that of conventional systems, in particular when operating in cooling mode.
In DE 10 2012 111 672 A1, a refrigerant circulation system of an air conditioning system is described for the conditioning of air in a passenger compartment of a motor vehicle. The refrigerant circulation system designed for combined operation in cooling and in heat pump mode as well as in reheating mode features a compressor, a heat exchanger for transferring heat between the refrigerant and the surroundings, a first expansion element, and a heat exchanger for transferring heat from the conditioned air in the passenger compartment to the refrigerant, a heat exchanger for transferring heat from the refrigerant to the conditioned air in the passenger compartment, and a second expansion element post-positioned in the flow direction of the refrigerant. The refrigerant circulation system is embodied to include a third expansion element with an adjustable flow area, which is configured and positioned in the refrigerant circulation system such that in a fully opened position, flow-through of refrigerant free of pressure loss is guaranteed, and such that with a reduction of the flow area, the pressure level in the heat exchanger for transferring heat from the refrigerant to the conditioned air in the passenger compartment can be adjusted via the pressure level in the heat exchanger for transferring heat from the refrigerant to the surroundings. The heat exchanger for transferring heat between the refrigerant and the surroundings, which receives air from the surroundings, is positioned in the front of the vehicle and can take in air from the airstream of the vehicle. When operating in cooling mode, the heat exchanger is operated as a condenser for dissipating heat from the condensing refrigerant to the surroundings, and when operating in heat pump mode, it is operated as an evaporator in order to absorb ambient heat. In particular when operating in heat pump mode at ambient air temperatures below the freezing point, the evaporation temperature is below the freezing point. When operating at temperatures below the dew point temperature, humidity from the air accumulating on the surface of the heat exchanger operating as an evaporator will freeze when the surface temperature falls below freezing temperature. The ice layer accumulating on the surface of the heat exchanger will grow, which has an adverse impact on the heat transfer, and therefore leads to a reduction of the power of the heat exchanger, and adversely impacts the efficiency of the air conditioning system.
In EP 2 716 478 A1, an air conditioning system for a motor vehicle with an enclosure featuring two flow channels separated from each other by means of a separation wall and a refrigerant circulation system are described. The refrigerant circulation system features two heat exchangers located inside the enclosure, as well as a heat exchanger located outside the enclosure. The heat exchanger located outside the enclosure can be operated between the ambient air and the refrigerant for heat absorption as well as for heat dissipation. The heat exchanger positioned inside the second flow channel can serve as a condenser for heat dissipation to, or as an evaporator for heat absorption from the refrigerant.
The systems known from DE 10 2012 108 891 A1, DE 10 2012 111 672 A1, and EP 2 716 478 A1 are what is known as air-to-air heat pumps, in which both the heat source and the heat sink is air.